Modular differential pressure transmitter/manifold for a fluid conveying pipeline

ABSTRACT

A transmitter manifold with integral transducer for measuring the differential pressure of a fluid conveying pipeline is provided. Interface modules are provided to provide for adaptability to a variety of user requirements. A sealing arrangement for the interface modules is also provided. In preferred form, the interface module includes a body having a flange portion and a neck portion extending outwardly from the flange portion, with the flange portion including holes for engagement with bolts threaded into the transmitter manifold.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of Ser. No. 871,560, filedJune 6, 1986, now U.S. Pat. No. 4,738,276, entitled "ModularDifferential Pressure Transmitter/Manifold for a Fluid ConveyingPipeline", and issued Apr. 19, 1980.

FIELD OF INVENTION

This invention relates to valve manifolds for differential pressuretransmitters.

BACKGROUND OF THE INVENTION

Differential pressure transmitters, as shown in FIG. 1, have long beenknown in the art. Typically, a differential pressure transmitter systemas shown in FIG. 1 is used with a pipeline 10 in which there is aflowing media which needs to be measured as to flow rate. A veryaccurate and economical method of measuring flow is to install anorifice 12 in the pipeline 10. Orifice 12 causes a differential pressureas media is forced through the small opening of orifice 12, whichdifferential is sensed by a transmitter 14 through process pressuresignal lines 16 and 18. The amount of differential pressure developed isa square root function of the flow rate. Consequently, by knowing thesize of the precision hole in the orifice plate, and by obtaining aprecision measurement of the differential pressure, the flow rate can becalculated with greater than 1% accuracy.

FIG. 2 illustrates the transmitter system shown in FIG. 1 in greaterdetail. It is conventional to provide a valve manifold 50 to interfacewith the two process pressure signal lines from the orifice 12 byutilizing gaskets 56, adapters 58 and nipples 60. Transmitter 14 is theninterfaced with the above valve manifold 50 with gaskets 68 and fourbolts 72 (one bolt shown in FIG. 2). In addition, a mounting bracket 74is provided with four bolts 76 (one bolt shown in FIG. 2) to bolt ontothe transmitter 14. Transmitter 14 is clamped onto a 2" pipe rack 78with U-bolt 80, which physically supports the hardware.

SUMMARY OF THE INVENTION

The present invention provides a novel transmitter/manifold for sensinga differential pressure in a fluid conveying pipeline. In one aspect ofthe invention, a valving arrangement is provided that allows forautomatic sequencing of the valves for all service functions. In anotheraspect of the invention, means for heating the transmitter/manifold isprovided to retain stability in sub-freezing conditions. In yet anotheraspect of the invention, interface modules are provided to provide foradaptability to a variety of user requirements. In still another aspect,the invention provides a novel sealing arrangement for the interfacemodules.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the invention and its advantages willbe apparent from the following Detailed Description taken in conjunctionwith the accompanying Drawings in which:

FIG. 1 is a perspective view of a prior art transmitter and interfaceapparatus;

FIG. 2 is an exploded perspective view of the apparatus of FIG. 1;

FIG. 3 is a partially exploded perspective view of atransmitter/manifold constructed in accordance with the presentinvention;

FIG. 4 is the transmitter/manifold of FIG. 3 rotated 90°;

FIG. 5 is a partially broken away side view of the transmitter/manifoldof the present invention;

FIGS. 6a-f are schematic representations of the valving of the presentinvention;

FIG. 7 is a partially broken away detailed side view of the valving ofthe present invention;

FIG. 8 is an end view of a blocking plug constructed in accordance withthe present invention;

FIG. 9 is a sectional view taken along the lines 9--9 in FIG. 8;

FIGS. 10a, 10b and 10c are views illustrating prior art adapterapparatus;

FIGS. 11a, 11b and 11c are views illustrating the modular adapters ofthe present invention;

FIG. 12 is a partially broken away side view of the adapter of thepresent invention;

FIG. 13 is a perspective view of an alternate embodiment of the adapterof the present invention;

FIG. 14 is a perspective view of another alternate embodiment of theadapter of the present invention;

FIG. 15 is an exploded perspective view of another embodiment of theadapter of the present invention along with a pipeline and transmitter;

FIG. 16 is a partially broken away end view of the adapter of FIG. 12;and

FIG. 17 is a sectional view taken along lines 17--17 of FIG. 16.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

I have invented an improved differential pressure transmitter/manifoldthat completely eliminates the unwieldly and expensive flow transmitterhardware package as explained above in connection with FIGS. 1 and 2. Myinvention makes it possible to eliminate all the interface hardware (14parts) between the two process signal lines 16 and 18 and the usersupplied pipe rack 78. The invention loses very little of thefunctionalism of the multipiece prior art system and gains considerablyin compactness and lower costs, and it eliminates the need for most ofthe parts shown in FIGS. 1 and 2.

A very important aspect of the invention is that the physical looks andfunctionalism of the prior art manifold valve hardware to which the useris accustomed is maintained. This is an important considerationnecessary to user acceptability. Thus, the instrument technician canapproach a familiar looking piece of equipment and has only to learnthat the instrument of the present invention includes the components ofthe flow transmitter within its body. The final "key to acceptability"is that he will learn as he services my instrument, or studies itsliterature, that by elimination the many interface parts listed aboveand shown in FIGS. 1 and 2 my transmitter/manifold loses nothing infunctional ability, service convenience, or reliability.

The improved transmitter system, as shown in FIGS. 3 and 4, includes aone-piece body 100 with process pressure connections 102 and 104 whichare the user input interfaces. The system output interfaces to the userare an electrical signal out port 106 and pipe rack 108 on which thetransmitter is mounted.

Body 100 includes saddles 100 to accommodate a vertical 2" pipe stand108 and saddles 112 to fit any horizontal 2" pipe stand. Also includedin the body are bolt holes 114 to receive U-bolts 116 to clamp body 100to the user's pipe stand 108 without requiring a separate bracket. Body100 also includes plugged ports 118 and 120 which can be used as purgeor drain ports. The plugged vent port 122 is also included and is usedin simultaneously venting the pressure on both sides of thetransmitter/manifold prior to servicing the sensor. Thetransmitter/manifold also includes a blocking valve 126 and a zeroingvalve 124 which, as explained below in connection with FIGS. 6a-f, allowthe service person to select any of the six service functions that wouldever be required. Also provided in body 100 are ports 128, 130 and 132,which provide access, as explained below in connection with FIG. 5, tosteam heat or an electrical heat system to control the temperature ofthe transmitter/manifold. Bosses 134 and 136 provide a means ofinstalling rod-out valves (as in my U.S. Pat. No. 4,391,289) to be usedto rod-out (unplug) the connections 102 and 104.

The provision of saddles 110 and 112 is an important feature of theinvention in that they serve as an excellent means to rigidly anchor thetransmitter/manifold on a 2" pipe. For extra versatility, the systemworks equally well on horizontal 2" pipe as well as vertical. Holes 114are of equal spacing such that U-bolt 116 can be installed eithervertically or horizontally to mate saddles 110 of 112. Saddles 110 arelocated to position the body away from the pipe support enough tominimize heat loss to the supporting structure. Often thetransmitter/manifold will be heated to avoid freeze-ups during coldweather. Saddles 112 are located to allow valve handles and other partsto clear the long 2" pipe, and again spaced out to reduce heat loss.

Ports 118 and 120 are located at the lowest point in the system and thuscan be used to drain any liquid collected in the system prior toservicing or recalibrating the system. They can also be used as purgeports when encountering a particularly dirty or plugging service, inwhich it is common practice to induce a small amount of clean media intothe system close to the manifold valves. This very small flow goestoward the dirty process media to keep solid particles from migratinginto connections 102 and 104 and causing them to become plugged.

Ports 138 and 140 have a dual purpose. When the transmitter/manifold isin a liquid service, it is mandatory to remove all vapor from thesystem. If one side of the transmitter/manifold or one of theconnections 102 or 104 coming to the transmitter/manifold had a bubbleof vapor trapped in it, the liquid head pressure on that side would bebiased and a false differential pressure signal would result. Ports 138and 140 are located at the highest point of the transmitter/manifoldporting, so all the vapor is removed when using these ports as ventports. These ports 138 and 140 are also positioned at equal elevations,and one on each end of the differential pressure measuringtransmitter/manifold. Thus, they are located where a technician wouldconnect his calibration kit to recalibrate the transmitter/manifold.

Ports 128 and 130 are part of an integral heating system, locatedadjacent the mounting saddles 110 and 112 which normally would be amajor heat loss to the system. Thus, steam injected into port 128 wouldmake up heat loss through saddles 110 and 112 and allow surplus heat tomigrate upward to keep the remainder of the system warm. Between port128 and port 130 is a condensing chamber 141, which in the preferredembodiment has a surface area of 0.122 square inches. Using 40 psi steamand a fiberglass-foam enclosure, this area provides protection for thesystem in a -25° F. temperature with a 15 mph wind.

Ports 102 and 104 can each be mated with one of interface adapters 142,144 or 146, as will be described in more detail below in connection withFIGS. 11a-15.

FIG. 5 illustrates an electric heating system which may be used as analternate to steam heating. This system has dual purposes: (1) to supplya compact and economical means for heating the transmitter/manifold toavoid a freeze-up, and (2) to allow thermostatic control of thetemperature changes of the transmitter/manifold. By controlling thetemperature, much greater accuracy can be maintained in that sensors andelectronics are all grossly affected by temperature change. This systemincludes, in the preferred embodiment, a 1/4" round, 200 watt, 120 voltcartridge heater element 200 which is hermetically sealed and insertedthrough port 132 into the boss built into body 100 between ports 128 and130. A bimetallic thermostat 202 is inserted into boss 204 to controlthe temperature to a preset temperature. Ports 128, 130, and 204 arelocated such that wiring connections 206, 208 and 210 between theheater, thermostat and the power loads can be made inside of such portsas shown. Either ports 130 or 240 (as shown) can become the port throughwhich power is brought to the system. The remaining ports are pluggedwith pipe plugs 212 to isolate the heating system from atmosphere.

Referring now to FIGS. 6a-f, another important feature of the newtransmitter/manifold is the design and porting of zeroing valve 126,blocking valve 124, and vent valve 122, which allow the servicetechnician to select any of six service functions. As shown in FIGS.6a-f respectively, the six service modes available are: NORMAL, ZERO,DEPRESSURIZATION, ISOLATION, CALIBRATION, and TEST E-UALIZEOR. Animportant feature of this invention is not just the ability to selectthese service functions, but that they are automatically selected in anexact logical order. The sequence of port closing and opening isautomatic such that the system actually protects the operator from theimproper sequencing problems encountered in the prior art manifolds thathave a group of many two-way (open or closed) valves.

Referring now to FIG. 7, zeroing valve 124 includes zeroing plug 250,packing 252 and packing nut 254. Zeroing plug 250 has a straight-throughpassageway 256, which connects high pressure instrument passageway 258and high pressure input passageway 260 in the normal position. In thezeroing position, shown in FIG. 7, zeroing passageway 262 connects highpressure instrument passageway 258 to equalizer passageway 246, whilehigh pressure input passageway 260 is blocked.

Similarly, as shown in FIGS. 7, 8 and 9, blocking valve 124 includesblocking plug 26, packing 268 and packing nut 270. Blocking plug 266includes a "T"-shaped passageway 272 which connects in the normalposition equalizer passageway 264, low pressure instrument passageway274 and low pressure input passageway 276, as shown in FIG. 7. Blockingplug 266 also includes a relatively small depressurize passageway 278offset approximately 45° from a branch of the "T"-shaped passageway 272as shown in FIGS. 8 and 9. In the depressurize position, depressurizepassageway 278 and "T"-shaped passageway 272 connect the low pressureinstrument passageway 274 and equalizer passageway 264, but low pressureinput passageway 276 is blocked. In the blocked position, both the lowpressure input passageway 276 and low pressure instrument passageway 274are blocked.

FIGS. 6a-f show the sequence of porting as valves 124 and 126 arerotated to the various positions. Special arrowhead-shaped handles 282and 284 (FIGS. 3 and 6a-f) retain the "pointing the direction of flow"feature of prior art lever handles while removing the objection of thesusceptibility of the lever handles being accidentally rotated by aperson kicking, bumping or snagging the handle.

NORMAL MODE (FIG. 6a). In the NORMAL MODE, both handles point in thedirection of straight-through flow similar to the convention set bylever handles on ball valves. High pressure input passageway 260 ofzeroing valve 124 is open and connected to high pressure instrumentpassageway 258, which allows pressure to pass from process pressure tothe high side of the instrument. Zeroing passageway 262 is closed whichcloses the equalizer passageway and allows pressure on the high pressureside of the instrument to be different than the pressure on the lowpressure side of the instrument. In the NORMAL MODE Of the blockingvalve 126, passageways 264, 274 and 276 are all interconnected as shownby "T"-shaped passageway 272.

ZEROING MODE (FIG. 6b). Referring now to FIG. 6b, to prepare theinstrument for zeroing, the operator selects the ZERO MODE by rotatinghandle 282 90° to the right. This blocks high pressure input passageway260 and opens high pressure instrument passageway 258 to equalizerpassageway 264, thus putting the low process pressure of port 276 onboth sides of the instrument. With the same pressure on both sides ofthe differential pressure instrument, its output should read zero. If itdoes not, the operator can adjust the instrument to do so by turning thezeroing screw supplied on all conventional flow transducers.

This invention protects the operator from improperly sequencing multiplevalves when shifting from the NORMAL MODE to the ZERO MODE. As "ZERO" isdialed, high pressure input passageway 260 first closes and then highpressure input passageway 258 is opened to equalizer passageway 264.This prevents serious problems that can occur on systems using a two-way(open or closed) valve for high pressure input and another two-way valvefor the equalizer connection. Specifically, the high pressure passagewayis controlled by a simple on-off (two-way) valve, the low pressurepassageway is controlled by an on-off valve, and the equalizerpassageway is controlled by an on-off valve, such that three two-wayvalves are utilized in contrast to my two specialized valves. In theconventional system, it is possible and not unusual for the operator toopen the equalizer valve before closing the high pressure valve, whichallows fluid to flow from the high pressure input through the equalizerand into the low pressure instrument line.

DEPRESSURIZATION MODE (FIG. 6c). About 90% of the service functionsperformed are checking zero as described above, but if further serviceis required, the instrument must be depressurized. The porting again issequenced automatically as the operator simply turns the blocking valve126 to its first position as shown in FIG. 6c. Both sides of theinstrument are then connected to the single vent valve 122 such thatwhile high and low pressure input passageways 260 and 276 are closed,high and low instrument passageways 258 and 274, zeroing passageway 262,equalizer passageway 264 and "T"-shaped passageway 272 are incommunication and connected to vent valve 122. Valve 122 can now beslowly opened to allow the pressure in the instrument to be relieved.

ISOLATION MODE (FIG. 6d). After the pressure is relieved, the nextlogical step is to continue turning the same handle 284 on around to itsfinal stop 90° from normal, which blocks low pressure input andinstrument passageways 276 and 274 and puts the instrument in ISOLATIONMODE (FIG. 6d). The instrument can now be safely removed or replaced.

CALIBRATION MODE (FIG. 6e). If the operator wishes to do a fieldcalibration on the instrument, he can put the instrument in theCALIBRATION MODE (FIG. 6e) from ISOLATION MODE by installing hiscalibration equipment to vent valve 122 and use it to controlcalibration pressures to the instrument. The porting is automaticallyset such that the signal coming into valve 122 from his calibrator willgo through open zeroing passageway 262 and high pressure inputpassageway 258 into the high pressure side of the instrument.

A very important feature of this invention is the natural, logicalsequence of turning handles 282 and 284 when servicing the instrument.The first step, regardless of what service function is to be performed,is to turn the zeroing valve handle 282 all the way against its onlystop--which is "ZERO". Any additional service requires moving theoperator's hand to the other handle 284 and turning it. The operatorneeds to pause at the "DEPRESSURIZE" position and open vent valve 122,then he continues turning that handle all the way against its "BLOCKED"stop for any further servicing. To return back in service, the sequenceis simply reversed. He turns handle 284 back to its stop at "NORMAL".This puts the instrument back into the ZERO MODE, which means processpressure is returned to both sides of the transmitter/manifoldsimultaneously. It is very important to avoid putting pressure back onone side and then the other side, because the instrument can be strainedand cause a loss of calibration--the very thing that was just set. Withconventional three valve manifolds with two-way valves, there is nothingto protect the operator from making this mistake. With my invention, theporting sequencing is done automatically and always in the proper order.To continue on back to NORMAL MODE, the zeroing valve handle 282 isrotated in the only direction it will go, i.e., toward the stop at"NORMAL".

TEST EQUALIZER MODE (FIG. 6f). The sixth service mode provided is theTEST EQUALIZER MODE (FIG. 6f), which is entered into when the system ispressurized and both handles 282 and 284 are set to "NORMAL". Theoperator simply turns the blocking valve handle 284 to "BLOCKED". Thiscloses the low pressure input and instrument passageways 274 and 276.Vent valve 122 is opened, and if media flows out of vent valve 122, thismeans that either zeroing passageway 262 or "T"-shaped passageway 272 isleaking into equalizer passageway 264. The service person may nowtighten packing nut 254 (FIG. 7) as required, which is used on thisvalve design to control inter-port leakage as well as valve stemleakage. When leakage is stopped, he can be assured that high pressurewill not leak to the low pressure side through the equalizer passageway204 when the instrument is in operation.

Because the instrument of the present invention has two handles, theonly mistake a service person can make is to turn the wrong handlefirst. This results in no harm and no change in the output signal he ismonitoring. If he then makes another mistake and turns the other handle,still nothing happens and no harm of any kind is done. Now his onlyoption is to turn both handles back and dial the correct valve to"ZERO". It is only then that the output signal he is watching willrespond and go to near zero output.

In contrast, the commonly used three two-way valve manifold has eightpossible combinations of open and shut valves which the operator couldtry. Of the eight, only one combination is right. Three combinations maylook right, but are wrong. One combination, all valves open, would seemlogically right and would look right on the output signal, but wouldcause a gross zero misadjustment if used, and it could cause damage tothe transducer as well as an unknowing removal of freeze protectionfluid in the process signal lines. When trying to get back to normal,four combinations would seem right by looking at the output, but bewrong. In summary, an operator better know what he is doing whileoperating a common three two-way valve manifold, while my design isself-educating and completely forgiving.

Referring now back to FIG. 3, another feature of this invention relatesto inlet interface ports 102 and 104 and interface adapters 142, 144 and146. The inlet ports 102 and 104 are threaded with 1/2" NPT threadedinlets 300 and, in addition, both ports also have threaded bolt holes302 to accommodate the bolting-on of an interface adapter 142, 144 or146. This versatility designed into the instrument is important in thatit relieves the purchasing agent of making detailed inlet interfacedecisions at the time of purchase, but it still leaves open the optionfor the user to choose any of the interface adapters he wishes or to usethe cheapest method possible, which would be 1/2" NPT threaded inlets300. Thus, any of the purchasing agent's and/or user's wishes,decisions, or lack of decisions about the type of inlet needed can besatisfied with this one transmitter/manifold inlet design augmented withthe availability of adapters 142, 144 and 146.

FIGS. 10a-c illustrate the conventional connecting apparatus used inconnecting process signal lines to flow or pressure measuringinstruments. Such apparatus is used in various industrial controlsystems and is universally used in chemical plants, refineries, powerplants and oil field installations. The two-bolt, oval flange adapter350 in use today is identical in basic design to an adapter first usedin the early 1940's. It is well known that there are problems caused bythese prior art flanges--especially in light hydrocarbon service or inservice with large temperature change cycles.

The inlet 352 of the flange 350 is threaded with 1/2" pipe thread. Mostusers presently use tubing instead of pipe, so male tubing connectorfitting 354 is purchased to adapt 350 flange to accept tubing 356.Stainless steel and other exotic metals are used for flange 350 andfitting 354, so the threads easily gall as fitting 354 is beinginstalled and leakage develops immediately or perhaps sometime later.Galling cannot be repaired and only grows worse as the installer triesto unscrew or tighten fitting 354 consequently, both flange 350 andfitting 354 are ruined and possibly dangerous fluid has leaked toatmosphere.

In addition, the two bolts 358 in the conventional apparatus are veryclosely spaced with respect to threads 352 and sometimes interferenceresults between the heads of bolt 358 and the hex portion of fitting354, as best shown in FIGS. 10a and 10b. This can cause a seriousproblem if the corners of the bolt head become damaged by an openwrench, because there is not enough room between the bolt heat andfitting to use a box end wrench.

A further problem relating to prior art apparatus concerns aconstruction requirement for some chemical plants and refineries thatall threaded connections be "backwelded" along weld 360 as shown in FIG.10c to prevent leakage. This specification is very close to impossibleto accomplish on the prior art two bolt oval flange adapters, becausethere is just not enough room between the bolt heads and the inlet pipeor male connectors or bolt 358. Many refuse to try backweld the flange,others try and fail to get a lead-tight weld, while only a few havemastered an expensive technique to accomplish a good weld 360.

Finally, another problem encountered is leakage of commonly used TFEgasket 362 (FIG. 10b), especially after the system has undergonesignificant temperature cycling, e.g., 32° F. up to 180° F. and back to32° F. The coefficient of thermal expansion of TFE gasket 362 is about10 times greater than steel. Consequently, as the system temperatureraises, gasket 362 will expand more than its metal retailer grooves 364in flange 350, which means it will extrude into central space 360between the port 102 and flange 350. As the system cools, the "memory"of TFE gasket 362 is insufficient to allow it return to its originalshape, so leakage results. To stop leakage, bolts 358 must be tightenedor a new gasket 364 installed.

Referring now to FIGS. 11a-c and 12, an additional feature of theinvention includes a one-piece interface module 400 which can be cast,forged and/or machined to a particular shape to satisfy certain cosmeticand functional parameters. The flange portion 402 has provision for twobolt holes 404 about 15/8 inch apart equally spaced on either side ofthe centerline of interface module 400. Upon surface 406 is machinedgroove 408, which is dimensioned to receive a gasket or packing ring 410(FIG. 12). FIG. 11b illustrates recesses 412, which allow the insertionof a box end wrench over the bolts 414. Bolts 414 pass through holes 404to fasten the interface module on to an appropriate instrument. Thelength of recesses 412 must be sufficient to allow insertion of astandard box and wrench or a deep-well socket over the heads of bolts414. Preferably, recess 414 is about 0.820 inch long to allow thisclearance for a 5/8 inch bolt. Appropriate diameters, dimensions,surface finishes, etc. of threaded end 416 are provided to acceptconventional nut 418 and ferrule 420.

Referring now to FIG. 13, with exception to threaded end 416 and the nut418 and ferrule 420, the description of interface module 400 above alsoapplies to the weld-type interface module 450. Interface module 450 isdesigned with a socket weld cavity 452 to receive a 1/2 inch pipe to bewelded in place. This arrangement completely eliminates the backweldproblems shown in FIG. 10c and explained above.

Referring to FIG. 14, a further embodiment includes interface module460, which includes all features of adapters 400 and 450 above, exceptcavity 462 is properly tapped for 1/2 inch NPT. This allows use of maletubing connectors, but without the interference of box-end wrenchproblems shown in FIGS. 10a-c and explained above.

My modular interface system of FIGS. 11a-14 includes a solid, one-pieceadapter to take the place of the old two-piece system shown in FIGS. 2and 10a-c. Even though it looks like a simple piece of hardware, it isthe result of research and development involving several parameters inseveral possible methods of use.

A further embodiment of the invention is shown in FIG. 15. Interfacemodules 470 have 1/2 inch NPT male pipe ends 472. This embodimentfacilitates mounting an instrument 473 directly on a 1/2 inch NPTthreaded ports 474 on meter run orifice flanges 476 o any other threadedoutlet on pipes, vessels or industrial equipment. The one-piece, compactprofile of interface module 470 results in an interface module that isstrong enough to withstand the continued stress of industrialenvironment while supporting the weight of my transmitter/manifold oreven much bigger instruments. The old two-piece flange and nipple system(FIGS. 2 and 10a-c) suffers a bad reputation today because of incidentsof very serious process blow-outs resulting from sudden fracture of thenipple 60 (FIG. 2). These fractures proved to be the result of metalfatigue often traceable to improper use of lightweight (schedule 40)nipples. Consequently, most users have removed from their list ofapproved procedures the use of the two-piece flange and nipple systemfor direct instrument mounting to orifice flanges, vessels, etc. If theuser wishes to close mount the instrument, he is now required to providea separate 2" pipe support system, which ruins the economics of closecoupling.

The embodiment of FIG. 15 includes the features of the above interfacemodules, except special provision is made to allow side by sideinsertion of two interface modules 470 into the two ports 474, which aretypical to what is found on orifice meter runs. Since orifice flanges476 and their associated gaskets vary in thickness, and ports 474 arenot drilled exact, the spacing of centerlines 478 can vary about 1/4inch from the standard fixed 21/8 inch centerline 480 dimensions. If thethreaded ends 472 of two interface modules are to screw into the meterrun with variable centerlines, and transmitter/manifold 473 with fixedcenterlines is to bolt onto the interface modules and seal pressure,three conditions must be satisfied simultaneously:

1. The ends 472 of both interface module 470 must be screwed into theorifice flange ports 474 far enough to allow the 1/2 inch NPT threads totighten and seal.

2. Simultaneously, the flange faces 482 of both interface modules mustbe sufficiently coplanar with respect to each other to allow gasket 484to seal as the one flat face of transmitter/manifold 473 is bolted ontothe two independent faces 482 of interface modules 470.

3. Simultaneously, bolts 486 and 91 must pass through bolt holes 488,whose centerlines vary, and screw into the mating threaded holes on thetransmitter/manifold whose holes are on exactly 21/8 inch centers 480.

On the old two-piece flange and nipple system (FIG. 2), it is requiredthat all three of these conditions be accomplished simultaneously byutilizing only one variable--how far the threaded end of the nipple isscrewed into the 1/2" NPT female connection on the orifice flange. The.centerline adjustment (condition 3 above) is accomplished by having thefemale 1/2 inch NPT connection offset about 1/8 inch with respect to thebolt holes. The sequence required to satisfy conditions 1, 2, and 3using the old two-piece system is as follows:

(a) Install nipples into flanges and tighten to hold pressure.

(b) Screw these assemblies into orifice outlets. Tighten to holdpressure.

(c) Lay straight edge across the faces of the two assemblies todetermine which one needs screwing in further to form a flat gasketsurface.

(d) Hold a transmitter/manifold up against the flat faces of the flangesand observe how much off the flange holes are with respect to the matingthreaded bolt holes in the transmitter/manifold body.

(e) Experiment by screwing in, 1/2 turn at a time, the flange-nippleassembly to allow the eccentricity of its connection to shift theflange's bolt hole centerline dimension to a usable 21/8 inch dimension.

The above procedure works if the installer is lucky and finds in step ethat no further adjustment is needed to accomplish a 21/8 inch boltcenter dimension. If further adjustment is required, he will of coursedisturb the adjustment made in step c to satisfy flat gasket surfacecondition 2. Each one-half turn required of the flange yields a lateralthread movement of that flange surface forty-three thousandths (0.043")of an inch. So it is possible that in step c above, he could not get theflatness closer than forty thousandths (0.040") of an inch from oneflange face to the other. If by chance the flange that needs screwing infurther to satisfy centerline requirements of step 3 above happens to bethe one that was already forced in more to satisfy condition 2 (step c),it will mean that after adjusting in step e that now the flatnessrequirement (condition 2) step c is far from satisfactory. Two one-halfturns of one flange causes a thread engagement lateral movement ofeighty-seven thousandths (0.087") of an inch--which is far too muchout-of-flatness allowable for the flange gaskets to function. This meansthat the other flange-nipple assembly must be also forced in a full turnto bring the flatness within limits.

One of the basic facts a pipefitter soon learns is that, especially onexotic metal piping, he cannot always force a joint one full turnwithout thread galling. Thread galling here would mean that not only thenipple, but also the entire, very expensive meter run assembly is ruinedand must be replaced or expensive backwelding repairs made in the field.

The interface module system of FIG. 15 was invented to eliminate theseproblems by the following features:

1. Interface adapter 470 is shaped such as to require only one pipethread make-up instead of the one on each end of the nipple like the olddesign. Since it is very difficult to manufacture better than a halfturn tolerance pipe threads, the two-piece design allowed a conditionwhere both ends of the nipple could be a half turn deep or shallow whichmeans the installed assembly could be one full turn shorter or longerthan the standard. As explained above, this can lead tofailure--especially if the pipefitter picked up one assembly that is oneturn too short to mate with one that is one turn too long.

2. By virtue of being a one-piece design, the possibility is eliminatedof a person mistakenly using a lightweight nipple and producing a hazardof the nipple being overstressed and breaking.

3. I have eliminated steps d and e above by providing elongated hole488, which allows one-eight inch of side to side (horizontal) movementof bolts 486 to attain the 21/8 inch bolt to bolt distance required toscrew into the transmitter/manifold body. Thus, the system can be usedwhen the distance between centerlines 478 is in the range of 17/8 inchto 23/8 inch. The need for the troublesome eccentric 1/2" NPT connectionon the flange is eliminated on this embodiment, and only conditions 1and 2 set forth above need to be controlled by the amount of threadengagement of each interface module. Condition 3 is automaticallysatisfied by the elongated holes 488.

As explained above with respect to FIG. 10b, a need presently exists forelimination of the TFE gasket 362 leakage after temperature cycling.There is a possibility that this problem will be enhanced by my newinterface module system used as in FIG. 15 because by nature of itsdesign, additional mechanical stress will be imposed on the gasket. Twointerface modules 470 will be screwed side by side directly into orificeflange ports 474. The transmitter/manifold will then be bolted directlyto the two interface modules with four bolts 486 and two seals 484. Thisresults in the weight of the transmitter/manifold being imposed uponseals 484 in addition to the stress of the bolts to hold the pressure.As shown in FIG. 12, the gasket is positioned between the interfacemodule and the transmitter/manifold such that all of the clampingcompressive forces of the bolts must pass through gasket. If theinterface modules support the weight of the transmitter/manifold as wellas forces imposed by vibration, or even a person stepping on thetransmitter/manifold while climbing on the equipment, the TFE gasketcould easily be stressed into the 1000 PSI range which results in a 17%cold flow or creep in 100 hours at 200° F.

Considering the possibility of shock loads of 3 to 5 times thismagnitude, it is clear that the TFE gasket design could present leakageproblems if pushed too far.

Metal to metal mating between the interface module and thetransmitter/manifold is desirable in that all of the loads of thetransmitter/manifold will be transferred directly to the interfacemodule without imposing any stress upon the seal. This of course,suggests standard o-ring seal technology. However, thechemical-petroleum industry is somewhat negative to o-ring seals becauseof incompatibility of o-ring elastomers and the users' chemicals. Mostspecifications by users call for 316 stainless steel parts and TFEseals. TFE will only work as an o-ring when special finishes aremaintained on the mating parts and the o-ring. This is difficult,expensive, and in fact would be impossible to control in cases where myinterface module would be used on some other supplier's transmitter.

Referring to FIGS. 16 and 17, an additional embodiment of the inventionincludes instrument 500 onto which is bolted interface module 502 in ametal to metal fashion. Bolts 504 are torqued to standards set for goodstructural fastening of flanges, which allows excellent physicalstrength between instrument 500 and interface module 502. Provided onthe face of adapter interface module 502 is a groove 506 which can be ofany convenient outside diameter and whose cross-sectional thickness andwidth is about the same dimension and is about equal to 0.120 times thediameter. Intersecting groove 506 at any convenient angle is port 508,whose total volume minus about four threads of packing screw 510 isequal to about 20% of the total volume of groove 506. Port 508 isthreaded with at least a 90% thread height for the full depth with anational fine thread pitch. Packing screw 510 is of equal pitch as port508. Screw 510's thread is 90% or greater, and its head can be of anyconvenient size and configuration, but its distal end should be groundflat and square with no chamfer. This will leave the last thread verysharp and coming to a feather edge. Common machining practice wouldrequire this easily damaged feather edge be removed, but here it isneeded to properly scrape the packing out of the threads of port 508 andpush it down and away from the packing bolt threads. Also provided is aperformed Grafoil® ring 512 which is pressed to about 50 pounds percubic foot density to conform to the dimensions of groove 510. Furtherprovided is a round slug 514 of preformed Grafoil® whose density is 35to 50 pounds per foot and whose dimensions conform to port 508 diameterto allow an easy slip-in insertion. The length will equal to port 508length minus about four threads.

The seal is assembled by placing the ring 512 in groove 506 and the slug514 into port 508. Interface adapter 50 is then bolted to the instrumentand packing screw 510 is tightened to the torque required to containleakage--usually about 50% of the call-out torque specified for thisbolt size in fastener tightening handbooks.

While specific embodiments of the present invention have been describedin detail herein and shown in the accompanying drawings, it will beevident that various further modifications are possible withoutdeparting from the scope of the invention.

What is claimed is:
 1. An interface adapter for connecting adifferential pressure transmitter manifold to a pipeline, comprising:abody formed of a non-resilient material; a flange portion of said bodyhaving a planar flange surface and elongated, partially cylindricalwalls perpendicular to the planar surface defining an upper hole and alower hole extending perpendicularly from the flange surface, the holesbeing vertically spaced on opposite sides of a medial portion of thebody and being elongated for side to side movement of the body withrespect to bolts extending therethrough; walls machined in the planarflange surface defining a groove dimensioned to receive a packing ring;a bolt surface coplanar with the planar flange surface and being locatedin the medial portion of the body; a neck portion extending outwardlyfrom the bolt surface; means for connection to the pipeline disposedupon the end of the neck portion; and the neck portion further includingwalls defining recesses associated with the holes, such that sufficientclearance is provided for a wrench placed over a bolt in one of theholes.
 2. The interface adapter of claim 1 wherein the neck portiondistal end includes a nut and ferrule to accept a tubing connection. 3.The interface adapter of claim 1 wherein the neck portion distal end isof socketweld configuration to allow insertion and welding thereon of apipeline.
 4. The interface adapter of claim 1 wherein the neck portiondistal end is threaded to accept standard threaded pipe.
 5. Theinterface adapter of claim 1 further comprising:a cylindrical walldefining a port intersecting the groove; and the port being at leastpartially threaded at an end opposite to the groove, such that sealingmaterial may be placed in the groove and in the port, and the sealingmaterial may be pressurized to seal the interface adapter to thetransmitter manifold by tightening a threaded member in the threads.